Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
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Re: Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
 
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It *is* difficult to build very narrow 8-pole filters with low loss.
That's one reason Elecraft offers a 5-pole, 200-Hz unit. 5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD dynamic range using the 200-Hz filter is outstanding. We've had some requests to offer a 270 or 300-Hz 5-pole filter, which would be better optimized for narrow-shift RTTY than the 200-Hz filter. We're also considering a dual-passband filter (500/270 or 500/300) that would fit in one slot. 73, Wayne N6KR On Jul 15, 2010, at 10:18 AM, Jim Brown wrote: > On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK wrote: > >> Agreed. 250-270Hz would be the "sweet spot" for an 8-pole filter, to >> guarantee good sales for the manufacturer *and* good performance >> for a >> range of users in heavy QRM. > >> Now let's see if Inrad or Elecraft take the bait :-) > > Hang on a minute, guys. Inrad builds a nominal 250 Hz filter, Elecraft > tests and re-sells it, and we buy it, because we've agreed that it's a > sweet spot operationally. > > The issue is that it's wider than than at the -3dB points. So the > problem appears to be that it's pretty difficult to build an 8-pole > 250 > Hz filter at 8.8 MHz, and that Inrad has given up on doing better. > > 73, Jim K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Jim Brown-10
Inrad currently offers an 8-pole 125 Hz at 5.7 MHz: http://www.inrad.net/product.php?productid=179&cat=100 |
Re: Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
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In reply to this post by wayne burdick
Lets really mess with contesters minds....give them a report of "20db over S2."
grandmaw Susan If you don't change direction you WILL arrive exactly where you're headed!! Susan Meckley, Skipper W7KFI-mm AFA9SM USSV DHARMA --- On Thu, 7/15/10, Wayne Burdick <[hidden email]> wrote: > From: Wayne Burdick <[hidden email]> > Subject: Re: [Elecraft] Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?" > To: "Jim Brown" <[hidden email]> > Cc: "[hidden email]" <[hidden email]> > Date: Thursday, July 15, 2010, 8:01 AM > It *is* difficult to build very > narrow 8-pole filters with low loss. > That's one reason Elecraft offers a 5-pole, 200-Hz unit. > > 5 poles is entirely adequate at these narrow widths. Our > 2-kHz IMD > dynamic range using the 200-Hz filter is outstanding. > > We've had some requests to offer a 270 or 300-Hz 5-pole > filter, which > would be better optimized for narrow-shift RTTY than the > 200-Hz > filter. We're also considering a dual-passband filter > (500/270 or > 500/300) that would fit in one slot. > > 73, > Wayne > N6KR > > > On Jul 15, 2010, at 10:18 AM, Jim Brown wrote: > > > On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK > wrote: > > > >> Agreed. 250-270Hz would be the "sweet spot" for an > 8-pole filter, to > >> guarantee good sales for the manufacturer *and* > good performance > >> for a > >> range of users in heavy QRM. > > > >> Now let's see if Inrad or Elecraft take the bait > :-) > > > > Hang on a minute, guys. Inrad builds a nominal 250 Hz > filter, Elecraft > > tests and re-sells it, and we buy it, because we've > agreed that it's a > > sweet spot operationally. > > > > The issue is that it's wider than than at the -3dB > points. So the > > problem appears to be that it's pretty difficult to > build an 8-pole > > 250 > > Hz filter at 8.8 MHz, and that Inrad has given up on > doing better. > > > > 73, Jim K9YC > > > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[hidden email] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
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In reply to this post by wayne burdick
Wayne,
I realize that I'm showing my ignorance, but could you briefly explain how a "dual-passband filter" works in the K3?? I would DEFINITELY be interested in either of the two possibilities you mentioned for my RTTY usage, even though the 8 pole 400 cycle one is pretty good. 73, Don, WB5HAK ----- Original Message ----- From: "Wayne Burdick" <[hidden email]> To: "Jim Brown" <[hidden email]> Cc: <[hidden email]> Sent: Thursday, July 15, 2010 1:01 PM Subject: Re: [Elecraft] Let's Try This Again -- was "[K3] ... A 750 Hz,8-Pole ... Filter?" > It *is* difficult to build very narrow 8-pole filters with low loss. > That's one reason Elecraft offers a 5-pole, 200-Hz unit. > > 5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD > dynamic range using the 200-Hz filter is outstanding. > > We've had some requests to offer a 270 or 300-Hz 5-pole filter, which > would be better optimized for narrow-shift RTTY than the 200-Hz > filter. We're also considering a dual-passband filter (500/270 or > 500/300) that would fit in one slot. > > 73, > Wayne > N6KR > > > On Jul 15, 2010, at 10:18 AM, Jim Brown wrote: > >> On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK wrote: >> >>> Agreed. 250-270Hz would be the "sweet spot" for an 8-pole filter, to >>> guarantee good sales for the manufacturer *and* good performance >>> for a >>> range of users in heavy QRM. >> >>> Now let's see if Inrad or Elecraft take the bait :-) >> >> Hang on a minute, guys. Inrad builds a nominal 250 Hz filter, Elecraft >> tests and re-sells it, and we buy it, because we've agreed that it's a >> sweet spot operationally. >> >> The issue is that it's wider than than at the -3dB points. So the >> problem appears to be that it's pretty difficult to build an 8-pole >> 250 >> Hz filter at 8.8 MHz, and that Inrad has given up on doing better. >> >> 73, Jim K9YC >> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.839 / Virus Database: 271.1.1/3007 - Release Date: 07/15/10 06:09:00 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
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In reply to this post by Jim Brown-10
> The issue is that it's wider than than at the -3dB points. So the > problem appears to be that it's pretty difficult to build an 8-pole > 250 Hz filter at 8.8 MHz, and that Inrad has given up on doing better. Sorry Jim, amateur practice has been to specify bandwidth at - 6dB not -3dB. Inrad use -6dB (within reasonable tolerance) for their other filters: AM (6 KHz): 6.250 @ - 6dB (+4%) 2.8 KHz: 2.880 @ - 6dB (+3%) 2.1 KHz: 2.175 @ - 6dB (+4%) 1.8 KHz: 1.838 @ - 6dB (+2%) 1.0 KHz: 1.063 @ - 6dB (+7%) 400 Hz: 450 @ - 6dB (+11%) 250 Hz: 370 @ - 6dB (+48%)!!! The problem is that "250 Hz" and to a lesser extent "400 Hz" is either marketing hype or an outright lie. I choose to believe it is an artifact of Yaesu's method of specifying filters bandwidth based on their cascaded bandwidth - in other words marketing hype. For example, the 708/704 pair provide an effective 250 Hz in cascade and 703/701 pair provide an effective 400 Hz at - 6dB in cascade. However, that means the 708 and 701 filters fail to perform to their nominal specifications when used by themselves. It's high time that INRAD admit to the marketing hype and produce a filter for the K3 that honestly lives up to its specified bandwidth values as a 250 Hz (+/- 5%) filter or change their marketing to admit that the "400 Hz" filter is really a 450 Hz filter and the "250 Hz" filter is really 370 Hz wide. The Elecraft produced 5-pole filters are generally specified correctly at -6 dB ... that it my four 500 Hz filters all measure between 480 and 510 Hz wide at - 6dB and my 200 Hz filters are both just slightly less than 200 Hz. If they can be specified correctly, why should INRAD be given a "pass" on truth in advertising? 73, ... Joe, W4TV On 7/15/2010 1:18 PM, Jim Brown wrote: > On Thu, 15 Jul 2010 14:53:10 +0100, Ian White GM3SEK wrote: > >> Agreed. 250-270Hz would be the "sweet spot" for an 8-pole filter, to >> guarantee good sales for the manufacturer *and* good performance for a >> range of users in heavy QRM. > >> Now let's see if Inrad or Elecraft take the bait :-) > > Hang on a minute, guys. Inrad builds a nominal 250 Hz filter, Elecraft > tests and re-sells it, and we buy it, because we've agreed that it's a > sweet spot operationally. > > The issue is that it's wider than than at the -3dB points. So the > problem appears to be that it's pretty difficult to build an 8-pole 250 > Hz filter at 8.8 MHz, and that Inrad has given up on doing better. > > 73, Jim K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by wayne burdick
Wayne Burdick wrote:
>It *is* difficult to build very narrow 8-pole filters with low loss. >That's one reason Elecraft offers a 5-pole, 200-Hz unit. > >5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD >dynamic range using the 200-Hz filter is outstanding. > Of course it is; but this discussion is about QRM at much closer spacings, sometimes occurring within the passband of a 350-400Hz filter. It is also about obtaining the maximum possible performance from the K3 under conditions of extreme QRM, which is sometimes strong enough to make the hardware AGC flicker on and off... at which point, the K3 fares less well. Under these extreme conditions, the DSP needs every possible protection from a tight roofing filter. I do have to keep emphasizing that word "extreme". Many people will never experience such levels of QRM because they have the good sense to run away... but contesters need to stay and tough it out. >We've had some requests to offer a 270 or 300-Hz 5-pole filter, which >would be better optimized for narrow-shift RTTY than the 200-Hz filter. It was I who initiated that request, for precisely the reasons outlined above (and further back in the archives [1]). Wayne kindly provided suggestions for a modification to increase the bandwidth of the 200Hz filter to about 270Hz, in order to accept more of the FSK sidebands and allow a few Hz more tolerance for calling stations. That filter has proved to be a true winner [2]. However, contesters are always looking for an extra edge, and a true 250-270Hz 8-pole filter with a steeper transition from the passband into the stopband would be the next step to try. As Joe, W4TV so rightly says, it would fill a genuine unmet need. 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek [1] http://lists.contesting.com/pipermail/rtty/2009-August/029397.html [2] The modification is to change both C3 and C5 in the KFL3-200A to 830pF (680 + 150pf SMD, in parallel). The filter schematic is in Elecraft's K3 schematics file. Details of the wider passband are at: <http://www.ifwtech.co.uk/g3sek/misc/kfl3-200_mod260.gif> Although Wayne provided helpful advice, please note that this modification is not officially supported or recommended by Elecraft. -- ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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I have to second EXTREME QRM.
One of the poison backlashes of really good antennas that have all that wunnerful transmit gain, is that it works REALLY WELL on receive. I have heard 9+30, 9+35, 9+40 and 9+45 signals on a calibrated K3. I have NO idea how they are doing that, or what magical propagation or combination of prop and power is producing these levels. But if you get one of these parked up 350 or 400, you can either give up your run frequency (which I think is why they do it) or you can GET SKIRTS. Dropping down to a real 250 roofer will not do it because you will not hear all the stations that call up and down more than that narrow passband. I'd say that overall a third of all callers will not call inside +/- 125 Hz. The 330 Hz 8 pole is just the thing. I have two in my dual RX K3 and one in my MP. They all measure the same. In the MP the 250 8 Mhz job and the 250 455 khz job ADD UP to a very clean sharp 250, which I think is where this filter first got its name. One of the tricks on the MP was to drop back from the 500 setting (which was really populated with an INRAD 400 hz pair) using the 400 455 filter and the 250 8 Mhz filter. This is about the same as using the 250(330) as a roofer and the DSP. No comparison on crushability of course. Back on the MP a 40 over up 350 meant you either gave it up or staggered Now those guys have K3's and they AREN'T moving. So either solve it with the 330 8 pole and 350 DSP width and NB on DSP 1-7 or 2-7, or leave. In ARRL DX went 4 hours and 290 contacts with one such up 380 Hz. I know he had to be having his ears smoked by my signal, so I also know he had a K3. This is also the answer for hams who live 6 blocks from one another. Get a K3 and live in peace. 73, Guy. On Fri, Jul 16, 2010 at 4:52 PM, Ian White GM3SEK <[hidden email]> wrote: > Wayne Burdick wrote: >>It *is* difficult to build very narrow 8-pole filters with low loss. >>That's one reason Elecraft offers a 5-pole, 200-Hz unit. >> >>5 poles is entirely adequate at these narrow widths. Our 2-kHz IMD >>dynamic range using the 200-Hz filter is outstanding. >> > Of course it is; but this discussion is about QRM at much closer > spacings, sometimes occurring within the passband of a 350-400Hz filter. > > It is also about obtaining the maximum possible performance from the K3 > under conditions of extreme QRM, which is sometimes strong enough to > make the hardware AGC flicker on and off... at which point, the K3 fares > less well. Under these extreme conditions, the DSP needs every possible > protection from a tight roofing filter. > > I do have to keep emphasizing that word "extreme". Many people will > never experience such levels of QRM because they have the good sense to > run away... but contesters need to stay and tough it out. > > >>We've had some requests to offer a 270 or 300-Hz 5-pole filter, which >>would be better optimized for narrow-shift RTTY than the 200-Hz filter. > > It was I who initiated that request, for precisely the reasons outlined > above (and further back in the archives [1]). Wayne kindly provided > suggestions for a modification to increase the bandwidth of the 200Hz > filter to about 270Hz, in order to accept more of the FSK sidebands and > allow a few Hz more tolerance for calling stations. That filter has > proved to be a true winner [2]. > > However, contesters are always looking for an extra edge, and a true > 250-270Hz 8-pole filter with a steeper transition from the passband into > the stopband would be the next step to try. > > As Joe, W4TV so rightly says, it would fill a genuine unmet need. > > > 73 from Ian GM3SEK > http://www.ifwtech.co.uk/g3sek > > > > [1] http://lists.contesting.com/pipermail/rtty/2009-August/029397.html > > [2] The modification is to change both C3 and C5 in the KFL3-200A to > 830pF (680 + 150pf SMD, in parallel). The filter schematic is in > Elecraft's K3 schematics file. > > Details of the wider passband are at: > <http://www.ifwtech.co.uk/g3sek/misc/kfl3-200_mod260.gif> > > Although Wayne provided helpful advice, please note that this > modification is not officially supported or recommended by Elecraft. > > > > > -- > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Let's Try This Again -- was "[K3] ... A 750 Hz, 8-Pole ... Filter?"
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In reply to this post by gm3sek
At that sort of bandwidth you are going to be clipping a non-trivial
amount of sideband power. Are you sure that a brick wall filter would be a good idea; I would wave thought it would cause significant dispersion. Ian White GM3SEK wrote: > > However, contesters are always looking for an extra edge, and a true > 250-270Hz 8-pole filter with a steeper transition from the passband into > the stopband would be the next step to try. > -- David Woolley Emails are not formal business letters, whatever businesses may want. RFC1855 says there should be an address here, but, in a world of spam, that is no longer good advice, as archive address hiding may not work. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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David Woolley wrote:
>Ian White GM3SEK wrote: > >> >> However, contesters are always looking for an extra edge, and a true >> 250-270Hz 8-pole filter with a steeper transition from the passband into >> the stopband would be the next step to try. >> >At that sort of bandwidth you are going to be clipping a non-trivial >amount of sideband power. Are you sure that a brick wall filter would >be a good idea; I would wave thought it would cause significant dispersion. > That theory only applies to the copy of weak RTTY signals against a background of noise. But when the main problem is QRM, the best *available* copy is obtained by reducing the bandwidth and accepting a small reduction in accuracy. The recommendation for a 250-270Hz filter is based on many years of practical experience in heavy contest QRM, starting with different combinations of cascaded filters in the FT-1000MP, and then moving on to different combinations of roofing filters and DSP in the K3. The measurable performance parameters have been certificates and a modest amount of silverware. With off-the-shelf roofing filters in the K3, the quality of RTTY copy in extreme QRM was inferior to the FT-1000. The 400Hz filter let in too much QRM which was routinely triggering the hardware AGC, while the 200Hz 5-pole required manual fine tuning for each new caller which made it unusable for serious contesting. With the modified 270Hz 5-pole, the performance of the two radios is now about the same... so the next logical step forward would be a 250-270Hz 8-pole, a "gaussian to 6dB" design with improved roll-off outside the passband. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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